To make a serious dent in your monthly utility bill, consider zeroing in on the biggest energy hog: your thermostat. The heating and cooling of your house accounts for half of your energy bill, especially when you're using an outdated system. Homeowners who upgraded to the Nest Learning Thermostat saved an average of 15 percent on cooling bills thanks to the system's abilities to be programmed from a phone, learn preferences and daily habits, and recognize via sensors when no one is home. Add another 12 percent saved on heating in winter, and the savings you earn pay off this smart home accessory in just two years. Everything after can go right into your vacation fund. Available on Amazon; $249.